Longitudinal segregation of Astyanax janeiroensis in Rio Ubatiba: a Neotropical stream of south‐east Brazil

Abstract –  In this study, we explored patterns of size and abundance of Astyanax janeiroensis in Rio Ubatiba (Rio de Janeiro, south-east Brazil) in relation to reproduction. A. janeiroensis broadcast their eggs in the water column throughout the year. Samples at seven sites conducted every second month from July 1994 to August 1995 revealed a predominance of larger adult specimens upstream and immature juveniles downstream. We hypothesize that upstream movements of adult individuals is a response to drifting of eggs and larvae.

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